Field of the Invention
The invention relates to a micromechanical component having a fixed micromechanical structure with a pair of capacitor plates and a movable micromechanical structure. The invention also relates to a microsystem on a semiconductor substrate with an integrated circuit and a micromechanical component. The invention additionally relates to a production process.
Micromechanical components are used for various purposes; one important field of application is that of proportional and non-proportional force sensors (acceleration and inclination sensors). The known sensors of that kind have fixed and movable micromechanical structures and are based on the capacitive measurement of the variation of the electrode spacing of a micromechanical capacitor. For instance, in the article by Sherman et al. in Conf. Proc. IEDM 92, page 501 (No. 0-7803-0817-4/92 IEEE), a structure is proposed in which a movable suspended polysilicon tongue is located between two fixedly mounted tongues. An acceleration changes the spacing of the movable tongue relative to the fixed tongues, causing the capacitance to one of the fixed tongues to increase and the capacitance to the other to decrease. That change is detected electrically.
In the production of such micromechanical components, there is great interest in processes that are compatible with the manufacture of integrated circuits, especially on a silicon substrate. Integrating micromechanics and trigger or evaluation circuits in microsystems is possible only if there is compatibility of the production processes. That is also important whenever existing semiconductor production systems are to be used to produce micromechanical structures as well. A process with which both an integrated circuit and a micromechanical component can be produced simultaneously in different regions of the semiconductor substrate, or in other words with which a microsystem can be produced with only minimal additional effort, besides that for the integrated circuit, would be especially advantageous.
For micromechanical components, the following production processes are known, among others:
a) Polysilicon Center Pin and Flange Process (M. Mehrengany, Y. C. Tai, J. Micromech. Microeng., Vol. 1, 73, 1991):
In order to produce the micromechanical structures following the production of the integrated circuit, such a process requires additional depositions of polysilicon after the metallizing complex. If the center pin process is to be performed before the integrated circuit is metallized, then the problem arises of etching the movable structures until they are exposed, i.e., laid bare, and simultaneously of protecting the insulation of the metallizing. Another disadvantage is the relatively high specific resistance of doped polysilicon.
b) Polysilicon-LOCOS Process (L. S. Tavrow et al, Sensors and Actuators A, Phys., Vol. A35, 33, 1992):
That process provides for making the movable micromechanical structures on a flat LOCOS oxide layer. Due to the temperature stress, the oxidation step can be performed only prior to the production of the transistors of an integrated circuit. If the entire process is carried out before the integrated circuit is produced, the resultant topology is unfavorable for the later steps, and the problem arises of protecting the micromechanical structures during the production of the integrated circuit. In an intertwined production process of that kind, the problem of etching the rotor in such a way that it is freely exposed while simultaneously protecting the circuit insulation oxides must be solved.
c) Selective Tungsten Process (L. Y. Chen et al, TRANSDUCERS '91, Int. Conf. on Solid-State Sensors and Actuators, San Francisco, Calif., IEEE Cat. No. 91CH2817-5, 739, 1991):
That process can be carried out following a circuit production process, but the proposed method does not solve the problems of electrical contacting and of protecting the metallizing insulation. The process is especially complicated and quite expensive because of the lithography steps.
d) LIGA Process (P. Bley et al, Microelectronic Engineering 13, 509, 1991; H. Guckel et al, Conf. Proceedings IEEE Micro Electro Mechanical Systems, Nara, Japan, 1991):
That process requires X-ray lithography and possibly later mounting of loose microscopic components.
None of those processes are configured in terms of their conception for the joint and in particular simultaneous production of an integrated circuit and the micromechanical component in a microsystem. They require a great number of layers and process steps, which serve solely to produce the micromechanical component, and are superfluous or even constricting or disadvantageous for the production of an integrated circuit.